$4.$ A positive integer is perfect if it equals the sum of all of its factors, excluding the number itself. Use a list comprehension and the following function factors: factors:: Int $->[$Int$]$ factors n $=[$x $|$ x $<-[1..$n$],$ n $$mod$$ x $==0]$ to define a function perfects:: Int $->[$Int$]$ that returns the list of all perfect numbers up to a given limit$.$ For example $($in GHCi$)$: $>$ perfects $500[6,28,496]$

Hint: define an auxiliary function that is perfect:: Int $->$ Bool which returns True if the given Int is perfect and False otherwise. Then use isperfect as a guard in a list comprehension to filter out all of the non$-$perfect integers, i$.$e$.,$ to keep only the perfect integers.